1. FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method for simulating corrosion activity and, more particularly, to an apparatus and method for simulating corrosion activity of process streams on process machinery.
2. DESCRIPTION OF RELATED ART
Corrosion in industrial and process installations is a major and continuous problem, particularly in chemical plants and petroleum refineries. Corrosion activity occurs within process machinery and transport lines to varying degrees depending upon such factors as the corrosivity of the process stream and its condensates, the temperature of the process, process velocities, and the metallurgy of the equipment employed in the process. Such corrosion activity can adversely affect the performance of process equipment, reduce the useful life of equipment and lines, and necessitate costly maintenance, repair and replacement of system components. Consequently, corrosion reduction, or at least the mitigation of the effects of corrosion, is a continuing concern in industry.
The establishment of an effective corrosion control program in a particular industrial installation begins with information on the corrosion activity expected or actually occurring within the installation machinery. Such information typically relates to the source of the corrosion taking place, the location of the corrosion activity, the type and rate of the corrosion activity, and the process parameters affecting corrosion initiation and propagation. One important source of corrosion is process vapors and their condensates. Many process vapor streams contain corrosive components that initiate corrosion upon condensation. Aqueous condensation leads to much of this corrosion activity and occurs primarily in heat exchange units and transport lines. The effects of such corrosion can be mitigated through the implementation of a corrosion control program that may include the use of corrosion inhibiting chemicals. However, the design, implementation, and optimization of such a program usually requires information on the corrosion activity itself.
A number of methods are known for collecting information on the nature of corrosion activity caused by process vapors and vapor condensates and on the process parameters affecting the initiation and propagation of corrosion. It is known, for instance, to insert corrosion probes into a process stream by mounting the probes directly in the process machinery or lines. While this method may supply information on corrosion activity actually occurring at the precise point of insertion, the probe placement will rarely correspond to the actual point of the worst corrosion activity, which often changes over time depending upon variations in process parameters. In addition, direct placement of corrosion probes in process equipment generally does not provide a profile of corrosion activity as a function of temperature and aqueous condensation.
Another method for determining corrosion activity of process vapors and condensates is simulation. As used in the present context, simulation refers to physical testing and analysis. In known corrosion simulators, a slip stream of process vapor is diverted and passed through a simulator circuit consisting in a prepiped bank of condensing areas or chambers. Water cools the vapor stream and causes aqueous condensation within the simulator. Corrosion probes, weight loss coupons, and condensate samples are then used to evaluate the location, type, and rate of corrosion taking place in the simulator. This corrosion activity is then related to the corrosion actually occurring or expected in the actual process machinery from which the slip stream was taken.
In one existing corrosion simulator a slip stream of vapors is circulated through a cooling coil positioned in a water box. Cooling water circulated through the water box in counterflow to the vapor stream causes aqueous condensation within the cooling coil. Corrosion and temperature probes detect corrosion activity occurring within the cooling coil. While this arrangement does provide information on corrosion activity and can establish a corrosion profile related to temperature, it is susceptible to operational difficulties, particularly the maintenance of the desired cooling water level and flow within the water box. In addition, the prepiped arrangement of the cooling coil and water box limit the adaptability of the simulator to a particular simulation application.
In another known apparatus for simulating corrosion activity, process vapor is circulated through a prepiped bank of condensers including a primary condenser and several smaller condensers. Cooling coils located in each of the condensers cause aqueous condensation of the vapor stream to simulate conditions in heat exchange units. The cooling coils am piped in parallel and take flow of cooling water from a header. The cooling water flow through each of the cooling coils is controlled independently to cause condensation at desired locations in the simulator and to generate a corrosion profile. Temperature and corrosion probes positioned in the condensers monitor corrosion activity and temperature. However, this simulator has a number of drawbacks. The various flow rates of cooling water through each cooling coil are difficult to control and coordinate, making a clear corrosion profile difficult to obtain. In addition, the prepiped arrangement of the simulator does not provide the flexibility needed to adapt the simulator to different simulation conditions and applications.
The present invention is directed to overcoming or minimizing the drawbacks of the existing techniques set forth above.